Mobile x-ray systems used in most operating rooms are used for a wide range of medical procedures including orthopedic, abdominal, and urological surgery, interventional procedures, vascular interventions, cardiology, neurology, and pulmonology. A mobile x-ray machine generally includes a large counter-balanced C-arm having an x-ray emitter (anode) mounted on one end of the C-arm and an image intensifier fluoroscopy tube on the other end of the C-arm. The C-arm unit is attached to a control unit that houses the necessary generator and electronic controls. The C-arm unit can be articulated in a variety of orbital, height, longitudinal, panning, rotational, and angular axes to properly position the unit for use in a particular medical procedure.
Although prolonged exposure to x-rays is dangerous, in years past, medical procedures were often performed using an x-ray machine that remained on continually during the procedure so that doctors and other medical personnel could see what they were doing. Upon the advent of laser-targeting devices, which aim a laser beam in the path of the x-ray beam, surgery and other operative procedures could be performed without continual x-ray exposure. The laser beam provides a visible target that aids a doctor in maintaining an accurate reference axis without continual operation of the x-ray machine, thereby reducing radiation exposure to doctors and patients. The ability to angularly align a laser beam in precise coaxial alignment with an x-ray beam is of paramount importance because slight discrepancies between the paths of the laser and x-ray beams will result in dangerous mistakes during delicate medical procedures.
Other laser targeting devices claiming to provide; coaxial laser beams have been developed in the past in attempts to aid medical operations under an x-ray machine. However, these prior art devices have at least two serious drawbacks. One drawback is related to the inherent problems with beam drifting that result from flexing of the C-arm, due to its weight, when the C-arm is articulated from one position to another. No prior art device allows an x-ray machine operator to compensate for this inherent beam drift by adjusting the angular alignment of the laser beam. Angular alignment, sometimes referred to as rotational alignment, is parallel, coaxial alignment along the entire length of the laser beam, which is necessary for the laser beam to precisely target a point on a patient under an x-ray machine. Prior art devices only provide for translational adjustment of the laser beam, which involves actually displacing the point source of the laser beam. Translational adjustment may ultimately focus a laser beam on the same remote point that an x-ray beam either focuses on or is emitted from (depending on which direction - the same or opposite, respectively - that the laser beam is emitted relative to the x-ray beam), but coaxial alignment is destroyed when the source of the laser beam is translated relative to the axis of the x-ray beam.
Another drawback of prior laser targeting device designs relates to the location of the focal spot of the anode. This focal spot is the point on the x-ray emitter coinciding with the central axis of x-ray emission. Prior art devices that target a laser by attempting to aim the laser at this focal spot often do so inaccurately because they aim the laser at the geometric center of the emitter, which may not precisely coincide with the central axis of x-ray emission. To accurately target a laser, the laser beam must be aimed at the exact focal spot of the anode, not simply the geometric center of the emitter.
U.S. Pat. No. 5,283,808 to Cramer et al. (hereinafter the '808 patent) discloses an x-ray device having a laser aiming system in an opposed configuration for use with a mobile C-arm x-ray machine. The '808 device comprises two basic components: a laser sight coupled to an x-ray emitter, and a laser housing coupled to an image intensifier.
One inherent problem with the '808 device is that adjustment of the direction of the emitted laser beam is accomplished only by translating the position of the laser beam relative to the image intensifier, which does not enable the device to maintain angular alignment of the laser beam with an x-ray beam. The '808 device reflects a laser beam off of a stationary mirror that does not provide a means for adjusting the direction of the laser beam striking the reflective surface. The '808 device uses only two adjustment screws to move the laser beam source in two orthogonal directions. Therefore, the '808 laser can only be adjusted in only two dimensions and always reflects off of the mirror in a direction perpendicular to the laser housing itself.
Another disadvantage of the '808 device is that its laser sight erroneously positions the laser target reference point in the geometric center of the emitter by providing a laser sight cap that snaps over an end of the emitter and latches in place. The '808 device therefore emits a laser beam that, first, is aimed at the geometric center of the emitter, which might not precisely coincide with the focal spot of the x-ray beam, and second, might not be perfectly coaxial with the x-ray beam, because the '808 device lacks the ability to angularly align the laser beam along the central axis of the x-ray beam.
Other laser targeting devices, such as the device disclosed in U.S. Pat. No. 5,031,203 to Trecha, are similarly flawed in that they have one or both of the aforementioned disadvantages. Until now, no laser targeting device correctly coaxially, angularly aligns the laser beam with the axis of the x-ray beam.